Hydrophilicity Control of Visible-Light Hydrogen Evolution and Dynamics of the Charge-Separated State in Dye/TiO2/Pt Hybrid Systems

Visible-light-driven H(2) evolution based on Dye/TiO(2)/Pt hybrid photocatalysts was investigated for a series of (E)-3-(5'-{4-[bis(4-R(1)-phenyl)amino]phenyl}-4,4'-(R(2))(2)-2,2'-bithiophen-5-yl)-2-cyanoacrylic acid dyes. Efficiencies of hydrogen evolution from aqueous suspensions in the presence of ethylenediaminetetraacetic acid as electron donor under illumination at λ>420 nm were found to considerably depend on the hydrophilic character of R(1), varying in the order MOD (R(1)=CH(3)OCH(2), R(2)=H)≈MO4D (R(1)=R(2)=CH(3)OCH(2))>HD (R(1)=R(2)=H)>PD (R(1)=C(3)H(7), R(2)=H). In the case of MOD/TiO(2)/Pt, the apparent quantum yield for photocatalyzed H(2) generation at 436 nm was 0.27±0.03. Transient absorption measurements for MOD- or PD-grafted transparent films of TiO(2) nanoparticles dipped into water at pH 3 commonly revealed ultrafast formation (